Method for securing burners



INVENTOR.

ATT ORNEY I GUY M. BAUDELET de LlVOS G. M. B. DE Llvols METHOD FORSECURING BURNERS Original Filed July 8, 1965 Aug. l5, 1967 mg 29m Si 552 w Nm United States Patent O s claims. (ci. 15s-117.5)

ABSTRACT OF THE DISCLOSURE A method for securing one or more of aplurality of burners supplying a common furnace, each burner having afuel supply pipe and an air register, which comprises shutting off theflow of fuel to the burner, closing the associated air register andblanketing the inlet side of the air register with an inert gas whichmay be recirculated flue gas.

` This is a division of application Ser. No. 470,413, filed July 8,1965.

This invention relates to a method and apparatus for operating burners.More particularly the invention relates to a method and apparatus forsecuring one or more of the burners delivering fuel and air to afurnace.

One object of my invention is to provide an arrangement for safely andeconomically tiring a furnace under partial load conditions with one ormore of the burners supplying fuel and air thereto secured.

Another object of my invention is to provide a simple, economicalarrangement for cooling the secured burners.

A further object of my invention is to provide an arrangement formaintaining the proper distribution of air for combustion in a furnacewhen one or more burners supplying fuel and air thereto are secured.

Sti-ll another object of my invention is to provide an arrangementwhereby a furnace having a plurality of burners may be operated with onepercent or less of free oxygen in the llue gas at partial load with oneor more of the burners secured.

A further object of my invention is to provide an arrangement preventingthe leakage of air through a secured burner into a furnace.

In accordance with my invention when a burner is secured, concurrentlywith the fuel and air thereto being shut olf an inert gas such asrecirculated ilue gas is substituted for the normal air supply. Thusleakage,if any, through the burner merely introduces an inert gas intothe furnace. The normal or desired excess air is then maintained at theoperating burners and in the furnace which is not the case withpresently available burners wherein a certain amount of air leakagenecessarily occurs through any secured burners.

Until recently the increase in excess air caused by air leakage into afurnace through a secured burner or burners -could be tolerated as itwas and is customary under present practice to operate a furnace at afairly high excess air in the order of 15% or more. Little or no effectis felt by slightly reducing the air-fuel ratio to the operating burnersto compensate for the air leakage through the secured rice burners. Orin the alternative, by maintaining the same air-fuel ratio in theoperating burners and permitting the furnace as a whole to operate at aslightly greater excess air. Recent studies have shown, however, that inaddition to increasing efficiency, the formation of deleteriouscompounds in the flue gas is retarded by operation at approximately zeroexcess air, that is to say operation at an excess air of 5% or less. Toaccomplish this it is essential that the correct air-fuel ratio bemaintained at all operating burners and air leakage through any burnerswhich are secured be eliminated. It is to a method and apparatus foraccomplishing these and other objects that my invention is directed.

Referring to the drawing, I show a furnace having a wall 64 in which aremounted a plurality, in the specic embodiment shown, three burners 57,5S and 59 supplied with air through individual windboxes 61, 62 and 63respectively. The air -for combustion is supplied the burner 57 througha register 66 positioned to the open or closed position by any suitabledevice such as a control drive 6'7 through linkage 68. A shut-off damper69 is mounted within a duct 71 through which air to the windbox 61 issupplied. The damper 69 is positioned to an open or closed position by a-control drive 72. In a similar manner combustion air to the burners 58and 59 is supplied through registers 73 and 74 which are positioned tothe open or closed position by a control drive 76 and 77 respectively. Ashut-off damper 78 positioned by a control drive 79 is provided in duct80 through which air to the windbox 62 is supplied. Similarly,combustion air supplied the burner 59 may be shut off by a damper 81mounted within a duct 83 and positioned by a control drive 82.

The air ducts 71, 80 and 83 are connected to a supply duct 84 which inturn is connected to one or more force draft fans, not shown, asconventional in the art. Disposed in the fuel supply lines to burners57, 53 and 59 are shutolf valves 43, 42 and 41 respectively. Fuel andair to burners 57, 58 and 59 may be regulated by positioning a damper 47by means of a control drive 48, and a fuel valve Ztl from a controlsignal derived from a conventional combustion control system, as commonin the art; or in the alternative, the dampers 69, 78 and 81 may be usedas combination control and shut-off dampers. Similarly valves 43, 42 and41 may be used both to control the ilow of fuel and act as shut ottvalves. In the latter case dampers 69, 78 and 81 as well as the valves43, 42 and 41 would be controlled from a signal derived from aconventional combustion control system and damper 47, control drive 48and fuel valve 20 omitted.

During normal operation more or less equal fuel flows to the burners 57,58 and 59 are maintained and variations in heat release obtained byadjusting in substantially equal amounts the `fuel ows to all of theburners. Simultaneously with changes in fuel flow, corresponding changesin air flow are made by parallel adjustment of the individual dampers69, 78 and 81 or in the alternative by adjustment of the force draftdamper 47. With the latter form of control, as previously explained, theindividual dampers 69, 78 and 31 are held in a Wide open position. Aswith burners presently available, whether for ring oil, gas or coal, therequired range in heat release cannot be obtained, it is customarypractice to operate with all burners in service from max. heat releaseto some predetermined lesser heat release when one or more burners aresecured to permit a further reduction in heat release.

At such time the fuel flow to the burner or burners being secured isshut-off and the associated air registers closed. Certain auxiliaryoperations may also be required such as withdrawing the burner tip, incase of oil ring, to prevent overheating, carbonizing of the fuelremaining in the burner, etc.

As heretofore explained air registers such as shown at 66, 73 and 74 arenot tight closing and accordingly air, while the burner is secured,passes through the burner and escapes into the furnace. Such air doesnot ordinarily enter into the combustion process as it is not properlymixed with the fuel discharged from the burners remaining in service.Also as it is customary to ratio total fuel to total air, the air`actually available for combustion at the burners in operation maydecrease. To avoid the consequence of operating with a deficiency Vofair and to provide a factor of safety, ordinarily the total air to totalfuel ratio is maintained higher than would otherwise be required. Recenttests have indicated that a high air-fuel ratio in addition todecreasing eiciency also results in the formation of harmful substancesin the products of combustion which rapidly deteriorate any surfaceswith which they are in contact and polute the atmosphere upon beingwasted.

In accordance with my invention the leakage of air through a securedburner is eliminated by sealing the inlet side of the closed airregister with an inert gas. In some cases the inert gas may be theproducts of combustion discharged from the furnace which are composedlargely of nitrogen and carbon dioxide. If the furnace is used to supplyheat to a boiler or other heat absorbing apparatus, preferably theproducts lof combustion (ue gas) are diverted to the air register afterhaving passed through such apparatus as the gases are then sufficientlycooled to avoid the necessity for auxiliary cooling, which mightotherwise be required. Thus referring to the drawing I show the inertgas as being drawn from a gas pass 46 of a boiler (not shown) justbefore the ue gases are wasted to the atmosphere. At such a point thetemper-ature of the gases may be in the order of 350 degrees F. or lessand relatively free of solids particularly if the gases have passedthrough a dust precipitator as is now common in the art. While I haveshown the gas pass 46 as forming the outlet of an economizer and airpreheater 45, it is evident that the inert gas may be obtained at any`desired point in the gas stream as, for example, after a dustprecipitator.

The diverted gas is passed through a duct 85 to a blower 86 whichdischarges into three branch ducts 88, 89 and 91 by way of a duct 87.Branch duct 91 discharges into the -air supply duct 71 between damper 69and register 66. Similarly, branch duct 89 discharges into duct 80between damper 78 and register 73. Branch duct 88 discharges into duct83 between damper 81 and register 74. The diverted gas is pressurized bythe blower 86 and maintained positive with respect to the forced draftair by a differenti-al pressure controller such as shown at 92 operatinga damper 94 through a control drive 93. Disposed in ducts 88, 89 and 91are shut-off dampers 99, 97 and 98 respectively, which are arranged tobe operated by control drives 102, 103 and 101 respectively.

When burners 57, 58 and 59 are in operation, dampers 97, 98 and 99 areclosed thus shutting olf the flow of inert gas to the burner registers.When however a burner is secured as, for example, the burner 57, damper98 is opened simultaneously with 'the closing of air register 66 anddamper 69. Thus the flow of combustion air is shut off and theregister66 sealed with the inert gas. Similarly, when burner 58 is secured airregister 73 and damper 78 are closed and damper 97 is opened and whenburner S9 is secured air register 74 and damper 81 are closed and damper99 is opened.

I show dampers 97, 98 and 99 arranged to be operated by control drives103, 101 and 102 respectively. As

evident to those skilled in the art, the teachings of my invention mayadvantageously be incorporated in an Automatic Burner Management Systemso that the operations I have described in securing a burner may beperformed automatically. Thus I show much an arrangement schematicallyfor burner 57 wherein a control signal, transmitted through a line 44,from a signal generator such as shown at 31 is arranged to operate fuelshut-off valve 43, register 66, damper 69 and damper 98. Such a controlsignal may be originated by an operator or automatically. Further, Ishow schematically a system whereby an overriding signal for securing aburner may be generated by a flame failure detector, such as shown at32, so that upon loss of ignition to the burner 57 the fuel flow theretois shut off and concurrently register 66 and damper 69 are closed anddamper 93 opened, thereby impressing on the inlet side of register 66the inert gas, which being above the pressure of the forced draft,effectively seals the leakage of air through the register and into thefurnace. Burners 58 and 59 may be similarly provided. I have not showncircuit details nor components as their inclusion is presumed and formsno part of my invention. T-hus it is obvious that a lock out device inthe circuit from the flame failure detector would be provided to allowigniting of the burner, etc.

As is evident from the preceding description, leakage of air into thefurnace through a secured burner is completely eliminated by theintroduction at the proper point into the air supply system of an inertgas such as pressurized recirculated flue gas. All secured burners areprevented from overheating by such'leakage of the pressurized inert gasas may pass through the closed register. In certain instances it may bedesirable to provide for a predetermined amount of leakage of the inertgas through the register to provide for such cooling. -Obviously manysuch changes can be made both in equipment and arrangement withoutdeparting from the scope of my invention `as set forth in theaccompanying claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. The method of securing one of a plurality of burners each discharginginto a common furnace and each haV- ing separate fuel and air supplymeans, which includes, shutting olf the flow of fuel and air to said oneburner and thereafter recirculating gaseous products of combustion fromthe furnace through said one burner into the furnace.

2. The method of operating a furnace having a plurality of burners toeach of which fuel and air is supplied to obtain a heat release lessthan the heat release obtainable with all of the burners in operation,which includes, shutting off the fuel and air to one or more of theburners and supplying recirculated ue gas in lieu of air to each of theburners to which the fuel and air supply is shut off.

3. The method of securing a burner having a fuel supply pipe and an airregister for admitting air to the burner, which includes, shutting offthe fuel to the burner, closing the air register and thereafterblanketing the inlet side of the closed register with an inert gas.

4. The method of operating a furnace having a plurality of burners eachhaving a fuel supply pipe and an air register for admitting air to theburner to obtain a heat release less than the heat release obtainablewith all of the burners in operation, which includes, shutting olf thefuel flow through the fuel supply pipe to one of the burners, closingthe air register of that burner and blanketing the inlet side of the airregister with an inert gas.

5. The method of claim 4 including the further step of obtaining theinert gas by recirculating flue gas from the furnace to the inlet sideof the air register.

6. The method of operating a furnace having a burner to which fuel issupplied through a pipe and air is supplied through a register uponflame failure, which in- 5 cludes, shutting oi the ow of fuel throughthe supply pipe, closing the air register and blanketing the inlet sideof the register with an inert gas.

7. The method of securing a burner to which fuel is supplied through apipe and air is supplied through a register from a duct having ashut-off damper, which includes, shutting oi the ow of fuel through thefuel supply pipe, closing the air register and the shut-off 6 8. Themethod of claim 7, which includes the further step of compressing theinert gas to a pressure above that of the air supply.

References Cited UNITED STATES PATENTS damper and introducing an inertgas into the air supply 10 FREDERICK L- MATTESON: JR Primary Examineductbetween 4the register and the shut-oif damper.

E. G. FAVORS, Assistant Examiner.

1. THE METHOD OF SECURING ONE OF A PLURALITY OF BURNERS EACH DISCHARGINGINTO A COMMON FURNACE AND EACH HAVING SEPARATE FUEL AND AIR SUPPLYMEANS, WHICH INCLUDES, SHUTTING OFF THE FLOW OF FUEL AND AIR TO SAID ONEBURNER AND THEREAFTER RECIRCULATING GASEOUS PRODUCTS OF COMBUSTION FROMTHE FURNACE THROUGH SAID ONE BURNER INTO THE FURNACE.